The synchronous frequency divider, shown in Figure 1, is considered more desirable than the asynchronous device
. Noise present on the input signal causes the time at which the triggering signal crosses its threshold to vary, resulting in phase jitter ([phi])(t)).
"This presents a problem for PC users because PCs are essentially asynchronous devices
. Using a traditional DSU/CSU with a PC requires special hardware interfaces and synchronous software.
Users employing the AS/400 improvements will be able to transfer data between the server and such asynchronous devices
as time clocks, badge readers, bar-code scanners, and robots.
According to Randy Ross, manager of RDS implementation, data-compression equipment has enabled the group to double the number of high-resolution graphics terminals on a single line, as well as linking both synchronous and asynchronous devices
over the same 9600-b/s line.
Attached asynchronous devices
can functions as IBM 3278 display stations, 3279 color display stations or 3287 printers.
The server can also be used to provide network users with access to modems and other asynchronous devices
An important consideration is that data PBXs are performance-efficient in providing data communications to low-speed asynchronous devices
, while LANs can provide both synchronous and asynchronous data communications.